A DeflectorPlane supports as the name suggests only a single plane of which particles can bounce of (see entry in Ogre manual).
Having particles bounce of arbitrary surfaces involves a lot of heavy collision detection and is therefore a task that is not in the responsibility of a rending but a physics engine, hence Ogre3D has no out-of-the-box support for this requirement.
But there are four different options in terms of already existing Ogre3D physics engine wrappers: Newton, Bullet, PhysX and ODE. Each of the wrappers has its own dedicated section in the Ogre Addons forum with further information and links.